A mineral magnetic characterization of the Plio-Pleistocene fluvial infill of the Heidelberg Basin (Germany)
A mineral magnetic characterization of the Plio-Pleistocene fluvial infill of the Heidelberg Basin (Germany)
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DOI：
10.1093/gji/ggx154
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发表时间：
2017-08
影响因子：
2.8
通讯作者：
S. Scheidt;R. Egli;T. Frederichs;U. Hambach;C. Rolf
中科院分区：
文献类型：
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作者：
S. Scheidt;R. Egli;T. Frederichs;U. Hambach;C. Rolf
海德堡盆地（德国）主要由河流沉积物组成的准连续沉积序列，具有成土叠印和湖泊夹层。这种松散的层序记录了第四纪和新近纪晚期一致的磁极性地层。以往的研究表明，硫化物和高矫顽磁性矿物是剩磁的载体。在这里，我们提供了一个扩展的矿物磁性研究的结果，旨在解开复杂的磁性矿物学。此外，我们评估了这些矿物作为古地磁信号载体的可靠性。对岩芯进行分析的一个主要障碍是从总长度为1 150米的岩芯中采集大量样本。对大量样品的快速测量只能提供有限的磁性矿物学信息。相比之下，时间密集型方法，如一阶反转曲线（FORC）或重复率分析，例如，产生了有价值的信息。所有分析的综合结果考虑了沉积物的异质成分，并表明了不同的古环境历史。上新世Iffezheim组是在交替的还原和氧化条件下形成的。磁铁矿、磁赤铁矿、赤铁矿和针铁矿是主要的磁性矿物。硫化物只有在特定条件下才能保存下来。更新世沉积物主要反映了沉积和成岩过程中的还原条件。已证明存在灰云母、黄铁矿和最有可能的磁黄铁矿。两者合计，我们的工作提供了一个详细的上新世更新世的环境磁记录，并阐明了河流为主的沉积序列进行岩石磁学研究的能力和局限性。
The Heidelberg Basin (Germany) hosts a quasi-continuous sedimentary sequence of primarily fluvial sediments with pedogenetic overprints and lacustrine intercalations. This unconsolidated succession has been shown to record a consistent magnetic polarity stratigraphy of the Quaternary and the late Neogene. Previous work has reported that sulphides and high-coercive minerals are the carriers of the remanent magnetization. Here, we provide the results of an extended mineral magnetic study that aims to disentangle the complex magnetic mineralogy. In addition, we assess the reliability of these minerals as carriers of palaeomagnetic signals. A major obstacle to the analysis of the drill cores was the large number of samples that were taken from a total core length of 1150 m. Rapid measurements on bulk samples provided only limited information on the magnetic mineralogy. In contrast, time-intensive methods such as first-order reversal curves (FORCs) or coercivity analyses, for example, yielded valuable information. The combined results of all the analyses consider the heterogeneous compositions of the sediments and indicate a varying palaeoenvironmental history. The Pliocene Iffezheim Formation was formed under alternating reducing and oxidizing conditions. Magnetite, maghemite, haematite and goethite are the predominant magnetic minerals. Sulphides were only preserved under specific conditions. The Pleistocene sediments reflect predominantly reducing conditions during sedimentation and diagenesis. Greigite, pyrite and most likely pyrrhotite have been shown to occur. Taken together, our work provides a detailed environmental magnetic record of the Plio-Pleistocene and elucidates the capabilities and limitations of rock magnetic studies performed on fluvial dominated sedimentary successions.